Jet engine noise suppression nozzles



Oct. 3, 1961 M. F. MUZZY EI'AI.

JET ENGINE NOISE SUPPRESSION NOZZLES 2 Sheets-Sheet 1 Filed Dec. 31, 1957 ('AL V/N 5.

Oct. 3, 1961 M. F. MUZZY EIAL JET ENGINE NOISESUPPRESSION NOZZLES 2 Sheets-Sheet 2 Filed Dec. 31, 1957 INVENTORS'. MUZZV PFAFMA/V W/LL/AM 5. Vol/N6 A rraezva 3 002,341 JET ENGINE Norsli SUPPRESSION NOZZLES Maurice F. Muzzy, Calvin E. Pfafman, and William E. Young, Seattle, Wash., assignors t Boeing Airplane Company, Seattle, Wasln, a corporation of Delaware Filed Dec. 31, 1957, Ser. No. 706,415 8 Claims. (Cl. 6035.6)

This invention relates to improvements in aircraft jet engine and similar nozzles for minimizing noise generation by the issuing jet stream. The invention is herein illustratively described by reference to presently preferred embodiments thereof; however, it will be recognized that certain modifications and changes therein with respect to details may be made without departing from the essential features involved.

Most of the objectionable noise generated by operation of a jet engine is that which originates in and around the discharging gases upon leaving the nozzle. Such noise is due to. the turbulence and shear effects caused by encounter of the jet stream with the atmosphere. It was discovered, as set forth in the copending patent applications of George S. Schairer, Serial No. 562,050, filed January 30, 1956, now abandoned, and William A. Reinhart, Serial No. 563,952, filed February 7, 1956, that large reductions of noise, particularly the more objectionable low frequency components, may be achieved by dis. charging the gases in certain patterns. Specifically it was found that large noise reductions were attainable by dividing the discharge into a plurality of materially separated streams or branches and permitting columns of outside air freely to enter and ventilate the spaces between those branch streams. The branch stream separation and the presence of atmospheric air therebetween greatly expedites the mixing, cooling and retardation of the issuing gases, and thereby not only reduces the total noise level but also shifts the frequency of remaining noise components largely into the upper portions of the audio spectrum where it attenuates rapidly in the atmosphere.

An object of this invention is to provide a noise suppression nozzle having improved means for maintaining separation of the branch streams and for expediting mixture of the gases therein-with atmospheric air. More specificallyit is an object to provide a means by which air is drawn and injected more effectively into the spaces between streams of a noise suppression nozzle for the described purposes.

A related object is an efficient multistrearn noise suppression nozzle configuration of the type employinggenerally radially disposed circumferentially separated branch streams; more specifically one permitting use of a tail cone or plug element to achieve nozzle divergence effect, but so formed that the central region behind the tail cone or plug element is efficiently ventilated by outside air for achieving increased noise suppression without reducing nozzle thrust materially below that of prior nozzles of the branch stream type having conventional tail cones.

Still another object is an efiicient noise suppression nozzle having annular shroud means which suppresses much of the shrill noise which develops by shear effect at the nozzle exit. A related object is the provision of such shroud means which, cooperatively with the nozzle proper, also serves as an ejector drawing outside air into the spaces between jet streams for increasing the stream ventilation and reducing shear effect, thereby further reducing noise.

Still another and more specific object is an improved noise suppression nozzle upon not only the low frequency noise regions of the audio spectrum but also upon higher frequency regions thereof.

Another specific object of this invention is a means by configuration which operates which, with negligible thrust loss, peripheral turbulence is created in the gas stream at the nozzle exit so as to expedite mixture of issuing gases with atmospheric air.

One feature of theillustrated preferred embodiment resides in the provision of a multistream suppression nozzle wherein the branch stream ducts are disposed to extend radially outwardly from a central tubular member terminated by an open-end tail cone or plug, together with means conducting outside air through nozzle passages for discharge through the tail cone opening. The resulting core of atmospheric air separating the radially inner portions of the branch streams not only helps to maintain separation between such streams but expedites mixing thereof with atmospheric air immediately downstream from the nozzle. At the same time the rearward taper of the tail cone or plug provides the desired nozzle divergence conducive to maximum thrust generation.

Another feature resides in the provision of vanes or vortex generating deflector elements mounted on the branch stream duct walls at the nozzle exit, preferably along the outer circumferentially extending walls thereof,

creating a peripheral fringe of turbulent gases and thereby promoting mixture ing air.

Still another feature resides in an annular shroud ring containing high-frequency sound absorption material, which shroud overhangs rearwardly beyond the nozzle exit outer edge and projects forwardly therefrom. This shroud is formed and situated in relation to the nozzle exit to intercept and absorb much of the very high-frequency shear noises developed by the encounter between the issuing gases and the surrounding air. A space is formed between such shroud and the nozzle rim, and into and through this space outside air of the jet stream, thereby increasing jet stream ventilation andreducing shear effect. 7

Still another feature of the preferred embodiment under discussion is the provision of bleed ports in the barriers or walls which separate and define the branch gas of the gas stream with surroundas e ector pumps increasing the rate of air movement. This ejector pump action further promotes noise suppression by creating turbulence in the moving air columns which enter the and thereby further with the gases.

Still other features reside in a corrugated nozzle configuration having corrugations of different sizes, providing suppression with respect to different portions of the noise spectrum, preferably in conjunction with a shearnoise ejector shroud and with air e'ection gas bleed ports as mentioned above.

Still another feature is the provision of liquid injector means by which liquid vapor is injected into the discharging gases, thereby cooling the same more rapidly and by the resulting volume reduction of the gases correspondingly reducing the total noise level thereof.

These'and other features, objects and advantages of the invention will become more fully evident from the following description thereof by reference to the accompanying drawings.

FIGURE 1 is a perspective view with parts broken away of the preferred embodiment incorporating certain of the above described features.

FIGURE .2 is a partial end view thereof from the rear aspect.

FIGURE 3 is a longitudinal sectional view with parts broken away showing the improved nozzle configuration as in FIGURES 1 and 2.

promote rapid mixture of such air is drawn by ejector action spaces between branch gas streams FIGURE 4 is a perspective view with parts broken away showing a second embodiment.

FIGURE 5 is a partial rear view thereof, and FIG- URE 6 is a longitudinal sectional view with parts broken away showing details of the second embodiment.

Referring to FIGURES l, 2 and 3, the illustrated nozzle has an annular flange 10 on its forward end adapted for attachment to the similar flange 12 mounted on the after end of the engine burner duct 14. An outer shell or cowl 16 surrounds the engine and laps over the flanges 1i) and 12 as illustrated. The outer nozzle shell 18 extends forwardly at a slight taper to the point of termination of the shell 16 and then for a short distance flares slightly to the flange 10, the fla'red'portion form.- ing a seat for the flanged lip of the shell 16. The engine includes a central island of tubular form which tapers rearwardly beyond the flanges 10 and 12 as indicated at 19, which island constitutes a rearward extension of the hub of the compressor drive turbine (not shown). The usual tail cone or plug 22 projects rearwardly from the island 19 along the longitudinal axis A. This rearwardly tapered plug or tail cone 22 is retained and serves a useful purpose in connection with the functioning of the improved noise suppression nozzle herein disclosed.

Exhaust gases discharging from the engine pass through the annular space 24 defined between the island 19 and the engine wall 14, and upon entering the nozzle proper are divided into branch streams or jets by the wedgeshaped flow dividers 26 which extend radially between the nozzle shell 18 and the central tubular member 29, the latter fitting over the plug 22 and projecting rearwardly beyond the tip of the plug. The flow dividers 2e are spaced apart circumferentially to form radially disposed flow spaces or orifices 28 which, at the exit of the nozzle, are separated by the considerable width of the flow dividers 26 so that the issuing branch streams are materially separated. In the illustration there are six such flow dividers and six flow spaces defined thereby, but it will be recognized that the number may vary. Each flow divider 26 comprises opposite side walls 266: and 2612 which extend generally radially between the members 18 and 2t) and which converge forwardly to a pointed leading edge 260. This straight edge 26c is inclined outwardly and forwardly in relation to the axis A by virtue of the slight forward convergence of the walls of plates 26a and 26b in relation to each other. Triangnllarly shaped openings 3% in the nozzle shell 18 at the locations of the stream dividers 26 permit outside air to enter the interior space defined between the forwardly convergent walls 26a and 26b of the respective dividers. Flow of outside air into and through these flow dividers is separated into two portions by a partition plate 32 which extends from the tubular member at an outward and forward inclination in relation to the axis A, to the outer shell 18, such plate being spaced rearwardly from the edge 26. This partition 32 extends transversely between the plates 26a and 26b in each flow divider, so that all of the air drawn into the hollow interior of each flow divider rearwardly of the partition 32. is discharged from between the rear edges of the walls 26a and 26b. The member 20 has openings 34 therein at the respective locations of the stream dividers, particularly the portions thereof lying forward of the partitions 32, so that air which is drawn inwardly through the flow dividers forwardly of the partitions 32 is discharged into the interior of the tubular member 29. All of the air entering through the openings 34 is discharged through the central opening of the member 20, the tail cone or plug 22 deflecting such air rearwardly as it enters the member 20.

By virtue of this nozzle configuration, the discharge from the nozzle comprises a plurality of radially extending branch streams which are separated circumferentially and by the width of the rearwardly tapered central member 20, serving as a tail cone or plug. The desired separation between these branch streams is maintained by flow of outside air through the spaces 28 and through the open end of the member 20.

Increased flow of air through the spaces separating the branch streams is achieved by the provision of bleed ports 36 formed in the side walls 26a -'and 26b of the respective rected along the path of flow of outside air entering the hollow interior of the flow dividers rearwardly of the partitions 32 therein and permit a small portion of the gases flowing through the spaces 28 to be tapped and to flow through the air ducts. The rapidly moving gases discharged into the air ducts by these bleed ports 36 have an ejector effect increasing the rate of flow of the air column, thereby further improving the gas stream ventilation. If desired, bleed ports may be provided in the walls 26a and 26b forwardly of the partitions 32 also, or at other locations where increased flow of outside air is desirable through the air passages of the nozzle.

Another feature of the invention resides in the provision of a sound insulating or absorbing shroud 38 of flat annular form surrounding the after end of thenozzle shell 13. The inside diameter of the shroud 38 slightly exceeds the outside lip diameter of the shell 18. The shroud ring projects rearwardly beyond the nozzle exit and extends forwardly to overlap the shell. Such shroud is supported from the shell by the posts 40 and 42 which project outwardly therefrom at suitable intervals. The spacing between the exit end of the shell 18 and the interior of the shroud permits outsideair to flow freely past the lip of the shell. Preferably, the annular space defined between the rearwardly flared shell 18 and the interior of the shroud has a slight taper which produces a scoop or ram effect. The shroud is so positioned that an ejection effect produced by the jet discharge pulls air through the annular space between the lip of the shell and the shroud and thereby reduces drag losses from the scoop or ram effect. As previously mentioned the shroud has a multifold noise-reducing action. An outtu'rned flange 44 surrounding the lip of the shell deflects the air slightly outwardly as itpasses the lip so as to cause some turbulence which further exp'edites the mixing of the air with the gases.

Preferably the shroud 38 is of hollow construction and is packed with glass fiber bat 46 or other sound absorption medium. Its inside wall is provided with perforations 48 which in conjunction with the packing material absorbs the shrill high frequency sounds which are generated primarily by shear effect at the nozzle exit.

Additional provision for rapid mixing of gas and air resides in the vortex generators or deflectors 49 mounted in each of the flow spaces 28, preferably along the outer walls thereof. These deflectors comprise substantially flat plates 49 disposed individually substantially perpendicularly to the outer wall defined by the shell 18. Each such plate, parallel to the others within the same group, is inclined slightly to the path of flow of gases through the corresponding space 28, thereby deflecting the gases near the outer periphery so as to create turbulence and improved mixing action. The proportion of gases deflected in this manner is relatively small, hence the nozzle efficiency is not appreciably reduced thereby. In order to avoid generation of torque about the axis A due to the presence of the deflectors 49 the direction of inclination of thme deflectors in half the groups of deflectors is reversed relative to that of the remainder so that the torque effects thereof cancel each other out.

Another feature of this embodiment i'sithe ring-like spray tube 51 which extends around the after end of the tubular plug member 20. Water or other suitable liquidis delivered to the spray tube 51 through supply conduits 53 from a suitable source (not shown). Holes 51ain the tube 51 discharge the water into the'jet stream. The spray from the nozzle 51 is directed into the discharge from the orifice even though'theope'ning's Slaface into flow dividers 26. These bleed ports are di-' the air stream emitted through the tube 20, becausethat air stream immediately swirlsinto contact with and turbulent mixture with the gases which emerge through the surrounding openings, as both come together beyond the lip of the tube 20. By delivering the water at a rate which, upon vaporization in the jet stream, materially reduces the streamvolume total noise level is correspondingly reduced. Such a device is thereby useful during short periods when flying near highly populated areas, although for long-term operation the carrying of an adequate Water supply to be useful presents a diflicult Weight problem.

In the embodiment shown in FIGURES 4, 5 and 6, parts which correspond to similar parts in the preceding embodiment bear the same reference numerals with a prime notation. A somewhat different nozzle configuration is employed for the channeling of outside air and for the production of the branched or multijet stream pattern ventilated by such air.

In this instance, the nozzle shell 50 is of a special corrugated form comprising circumferentially spaced deep and wide corrugations 50a separated by groups of narrower and shallower corrugations 50b. The depth of these corrugations in the radial sense is maximum at the nozzle exit and is reduced progressively toward the forward end of the nozzle, so as to achieve rearward taper effect in the shell. correspondingly, the width of the corrugations circumferentially is tapered slightly toward the rear of the nozzle.

The radially disposed side walls of the large corrugations 50a are in some degree equivalent to the radially disposed stream divider walls 26a and 26b in the preceding embodiment insofar as they separate the jet discharge into branch stream portions and permit outside air to flow along the exterior of the shell 50 and into the spaces between these large branch stream portions. Similarly the side walls of the smaller corrugaitons 50b produce additional branching of the stream pattern and provide outside air flow in the spaces between these smaller branches, around the fringe of the tor bleed ports52 are provided in the shell forwardly of the exit thereof, especially in the large corrugations 50a in order to discharge some of the engine gases rearwardly into and through these corrugation spaces for increasing the air flow by ejector action and thereby improving the ventilation of the stream pattern.

The provision of large corrugations separated by groups of small corrugations has the effect of suppressing audible noise in different portions of the spectrum. The large corrugations tend to suppress low frequency noise components whereas the small corrugations tend to suppress the higher frequency components in the spectrum.

Surrounding the shell and projecting somewhat beyond the exit end thereof is a noise absorption ejector shroud ring 54 somewhat similar to the shroud 38 in the preceding embodiment. In this case the shroud 54 is relatively wide and flat, i.e., extends along a considerable portion of the length of the nozzle, and it has a rearward taper so that the annular space defined between the shroud and the shell is relatively wide in the radial sense at the forward edge of the shroud and decreases considerably in width toward the after end thereof. The shroud 54 is supported by the posts 56 and 58 arranged at intervals around the nozzle and is constructed with a perforated inside wall and a solid outside wall, between which sound absorption material 60 is packed as before. The rearward taper of the annular space defined between the shell and the nozzle has an air scoop or ram effect which, aided by the ejector action of the jet in cooperation with the shroud, effectively both forces and draws outside air into the jet stream and thereby further improves ventilation of the stream pattern as in the first described embodiment. As before, the additional functions of the shroud 54 are to absorb high frequency noise generated by shear effect at the nozzle exit, and also to reduce jet pattern. Preferably air ejecabout the amount of shear effect noise, such reduction being due to the reduction of relative velocity of shear between jet gases and surrounding air by virtue of the rearward acceleration of the air as it is ejected past the nozzle orifice within the ejector shroud.

From the foregoing description it will be recognized that certain features of the invention relate to the suppression of noise by improving the rate of ventilation and mixing of the branched stream pattern by and with outside air, certain others relate to the reduction and absorption of high frequency noise generated by shear effect at the nozzle exit, and still others relate to the production of turbulence of gases and air in the boundary regions therebetween. The overall objective achieved by these improved nozzle configurations is of course to provide practical nozzles adapted to suppress engine noise without materially reducing thrust and aerodynamic efficiency. It will be recognized that the principles of the invention may be carried out in nozzle forms not only as shown and described herein but in modified types of construction as well.

We claim. as our invention:

1. A jet engine noise suppression nozzle comprising branch duct means opening rearwardly from said nozzle and forming a plurality of separate engine exhaust gas a central region to discharge a plurality of jet streams separated from each other circumferentially, said nozzle being formed with outer side openings permitting rearward and inward flow of outside air into the circumferential spaces between adjacent jet streams, central duct means forming a rearwardly directed central flow opening situated within the region about which the separate discharge orifices are grouped, and a plurality of duct means arranged in the nozzle in longitudinal alignment with the spaces between jet streams to collect and guide outside atmospheric air to said central duct means to permit such air to escape rearwardly through said central flow opening, thereby to effect mixture of air with the jet streams on the inner sides as well as on the outer sides and the mutually adjacent sides thereof.

ing an outer nozzle shell with side openings therein, and wherein the central duct means comprises a tubular member, and wherein the branch duct means comprise pairs of duct side walls extending generally longitudinally and generally radially between said outer shell lar member, the members of each pair being intercom nected forwardly of the nozzle exit plane and being spaced apart with an opening opening for rearward discharge of air between said members of each pair, the mutually adjacent side walls of adjacent pairs being spaced apart at the exit plane and forwardly thereof to define rearwardly open flow spaces therebetween for rearward discharge of gases between said interconnected pairs and a plurality of air duct means opening outwardly through the side of said outer shell and leading rearwardly and inwardly, at the circumferential locations of the respective branch duct wall pairs, into said tubular member for conducting outside air into said tubular member and discharging such air rearwardly therethrough, thereby to ventilate the central region between the discharges from said branch duct means.

3. The jet engine defined in claim 2, wherein the mutually adjacent members of the adjacent pairs of side walls converge forwardly in relation to the nozzle to form wedge-shaped stream-splitting forward portions, and wherein the air duct means are defined by the internal space formed between the forward portions of the mutually convergent side walls and by a partition extending transversely between such convergent side walls and extending generally rearwardly and inwardly from said outer shell to said tubular member, thereby to divide the 2. The jet engine defined in claim 1, further compris.

and said tubutherebetween, at the exit plane, which communicates with an associated nozzle side 7 space between each said pair of convergent walls into a rearwardly opening air flow space, aft of said partition, and an air duct space conducting air into said tubular member, forwardly of said partition.

4. The jet engine defined in claim 8, and an ejector pump means comprising gas bleed ports including openings in the duct side walls and formed and arranged to discharge a relatively small proportion of the exhaust gas from the engine generally rearwardly into the circumferential spaces formed between the branch duct means, thereby to increase the rate of air flow through such spaces.

5. The jet engine defined in claim 1, and air ejector pump means comprising gas bleed ports formed and arranged ltO discharge a relatively small proportion of the exhaust gas from the engine generally rearwardly into the rearwardly directed air discharge openings formed by the mutually adjacent walls of the branch duct means, thereby to increase the rate of air flow through such spaces.

6. The jet engine defined in claim 2, wherein the incombustible liquid injection means comprises a nozzle means adapted to be connected to a source of incombustible liquid and located at the end of the central duct tubular member and having liquid discharge openings therein.

7. The jet engine defined in claim 1, and shroud means comprising a substantially annular member surrounding and spaced outwardly from the discharge duct means in coaxial relation thereto to define an air flow space between said shroud and branch duct means through which air may flow, said shroud means being relatively thin in a radial sense and overhanging rearwardly beyond the discharge end of said duct means and extending forwardly into overlapping relationship with the duct means, said shroud means being arranged cooperatively with the nozzle duct means to form a rearwardly divergent air flow space ltherebetween in any of diiferent longitudinal planes containing the nozzle axis, thereby to eject outside air rearwardly and inwardly into the spaces between jet streams.

8. A jet engine noise suppressison nozzle comprising branch duct means opening rearwardly from said nozzle and forming a plurality of separate engine exhaust gas discharge orifice openings grouped about a central longitudinal axis and spaced apart in a circumferential sense about a central region to discharge a plurality of jet streams separated from each other circumferentially, said nozzle being formed to permit flow of outside air into the circumferential spaces between adjacent jet streams, central duct means forming a rearwardly directed central flow opening situated within the region about which the separate discharge orifices are grouped, and duct means arranged to collect and guide atmospheric air to said central duct means to permit such air to escape rearward'ly through said central flow opening, thereby to effect mixture of air with the jet streams on the inner sides as well as the mutually adjacent sides thereof, said nozzle further comprising an outer nozzle shell, the central duct means comprising a tubular member, and the branch duct means comprising pairs of duct side walls extending generally longitudinally and generally radially between said outer shell and said tubular memher, the mutually adjacent side walls of adjacent pairs being spaced apart and defining a rearwardly open flow space thercbetween for passage of air rearwardly therethrough, said otuer shell having openings therein permitting entry of outside air into said flow spaces, and air duct means opening through said outer shell and into said tubular member for conducting outside air into said tubular member and discharging such air rearwardly therethrough, thereby to ventilate the central region between the discharges from said branch duct means, the mutually adjacent members of the adjacent pairs of side walls converging forwardly in relation to the nozzle to form wedge-shaped stream-splitting forward portions, the air duct means being defined by the forward portions of the mutually convergent side walls and by a partition 7 extending transversely between such convergent ,side

walls and extending generally outwardly between said shell and said tubular member, thereby to divide the space between such convergent walls into the rearwardly opening flow space, aft of said partition, and an air duct space conducting air into said tubular member, forwardly of said partition.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Aviation Age, Jet Noise Can Be Cut," by Withington, vol. 25, No. 4, April 1956, pages 48-53.

Flight, Reduction of Jet Noise, vol. 68, No. 2424, July 8, 1955, pages 57-66.

Alford: Abstract of Ser. No. 104,281, published May 20, 1952, (658 0.6. 916). 

